Short-pulse modulator



Jan. 19, 1954 Filed Oct. 12, 1945 INPUT FROM BLOCKING OSCILLATOR H. JOHNSON EI'AL 2,666,849

SHORT-PULSE MODULATOR 2 Sheets-Sheet 1 FIG! VOLTAGE INVENTORS HAROLD' L. JOHNSON VERNAL JOSEPH SON ATTORNEY 2 Sheets-Sheet 2 Filed Oct. 12, 1945 S mNN mama-L ww NNH E HP W .0 LJ DI- mm L RR W Hv mm A mm mm mm 7: EUUUFE- ATTORNEY Patented Jan. 19, 1954 a OFFICE I 121666,!!49 SHEET-PULSE MODULATOR -llarolii305115011, Pasalilena, 'CaIiiZ, a'nii Vernal iroseiahsio'n, Cambridge, Mass.

cappiiomiiin october -12, 1945, Serial :No. 6225053 ulator syst ms employed de ay l nes, so ca d,

which s or d up en r y be ween puls s nd relea d i hen trig ered in h iorm subs ntially of a sq re wave or fia -topp d :p lfifl ut ut. The present invention :progiuoes a sin le narrow flat top ipulse why saturation clipp n f 12 18 hi a plitude ry row first posit r swin f a Shock "e c t d L-C circu and y most oo p te-lr pin t e remain ng s iiletionsefthe L-C circuit. I;h is narrow ipulseis then used to feed a driver amplifier capable o f iijurnishin the r quir d po t the p o r voltage 150 .-hmeenetrori with which it is being used.

-It -is the prinoipal object of -this invention to provide a modulator 'oircuit -for eprociucing high amplitude fiat -tqpped pulses :of very short durafiOn with a steep leading trailing edge whenever -the circuit irig gered.

It; is another object'toproduce narrow rectan gular pulses by use of a shook-excited and damped LQC circuit, and ah overdriven amplifier.

"O'fiher ob" (its "and "features may be fou'nti in the foiIowiii'g "detailed tecserip'uon "when taken with the figures,

Fig. 1 isfa 'eireuit diagram "for illustratin the principle "cf the iri'v'erition;

Fig. 21s a Waveform"showiiig'substanfially the shape of the "pulse "going into "the 'ci'rive'r stage, and showing the "output ulse; and

Fig. 3 "is a complete "circuit diagram of one embodiment "of the invention.

Rferririg'n'ow to Fig. lthere issiio'wn*'at hyratron tuire 2. 'A large fastrisirigf volfiage pulse is applied to the grid or ibis tub'e 2 impugn ecu"- "pliri'g capacitor from'--b1o"c" kiu;g osciiiat'ors (not shown) t'rigeered et the kie'sired rp'etition rate. This minimizes the delaly in fi'rin'g time as" Well 'a-s range jitter due to variations in firing tirne. variation of the delay in firing isifne siiould be i-elatix elyisfirallcompared"to thei'puiseuvidth.

When a 5 pulse is desired} th ahiockingmsciliator 2 (not shown) triggers the thyra'bron -2 causing ia large current to flow :throueh inductor '6 which is wound on :the'same form a s=ind-uctor 8-for*o1os'e mutual coupling between these two inductors. The inductor 8 is designed to'tunewith st-rayand tube capacitances a Wave length which is approximately 'twice *the desired pulse length. For instance, for a 0.1 microsecond pulse the -fi e-=- quency would be fi meeacycies ipe1'='S C0hd,a I IdfOr a pulse .03 microsecondiongthevfrequency would beabout 17 megacyoles per second. 'el he'primary is tuned. to a considerably lower :fre'quencyamlds The current in inductor 6 would normally :take the form of damped. voscillations but'thereis -ineluded a diode I O across the-secondary iindue'ior -8 which dumps 'this res'onanticircuit very heeivil-y on the ne ative swing. The inductor coils-.5 and'B are connected in such a mamrerthat the fi'rst --swing is positive. When i'point becomes .positive with respect to point M, thexiiiode *5 ii is inop erative and iihis positive swing exciiies a driver tube 16.

In Fig. 2 there shown an :auproximabion of the wave form appoint 42. By using this vpulse oo "drive a boot strapped driver tube 4% beyond -s'aturation -the resulting. output can be made square top'ped as shown in Fig. 2 by ehie domed line 18. The boot strapped driver including :ithe tube 16 is simply a cathode :loaded iamplifier where the input is coupled direc-tl'y racross ehe grid and the cathodeand 'iihe cathode :isireturned to ground or other reference :potential :gpoint through a cathode 'load umneciance. The .eerm "boot strapped has been used because an in-- crease of :grid voltage increases 'the cathode voltage and the oathode -vol-tage riseurther increases the grid to-groundvoltage,

The output pulse i8 is fed'directl-y to these'rids of a i pair-of modulator tubes (not'ehowufiu-Fig. 1). The output 'from'thmplates'of these cubes is fed to the magnetrenrnobshown).

Fig.3 shows the compieteeircuit; diagram .of a

short :puise =modu1ator -eomprisiug =-two bloeking oscillators 2!] and 22 :connectediin series which produce -a sharply rising triggerzpuls'eonzthergrid of a =thyratro'n tube 24 in response iao I a positive '-trigger input 6011118 primary 2-5 of thefirst blocking oscillator transformer. This'causes tube 12.4 to conductsharply causirig currentz-toflowlthrough the primaryrinductor'flifi which is-cioselyzcoup'ied inductor 218 is tuned to resonate with -thestray and tube capacitanees a t i a frequency such i that the first half cycle -;of =osci11atien E'ELDPIQX-ilfifitfiii 3 the desired pulse length. Across the tuned L-C circuit 28 is a diode 30 which almost completely damps out the succeeding negative swing and oscillations which would normally follow.

The first positive swing is fed to the grid of a tetrode tube 32, sending it beyond saturation so as to produce a squar topped wave. This stage is a boot strapped driver with an output to a pair of modulator tubes 34 and 36 in parallel whose plate pulse is employed to drive a magnetron (not shown). Also included in the magnetron circuit are a meter 31 for measuring the magnetron current and a damping resistor 38 for preventing overshoots of the magnetron exciting pulse. In the cathode circuit of the driver tube 32 is included a peaking inductor 33 which assists in squaring the pulse by decreasing the rise time of the leading edge. The value of inductance 33 must be carefully chosen to accomplish this without at the same time producing a spike on the leading edge which would be detrimental to smooth magnetron operation.

Whereas the earlier systems for producing modulator pulses did so either by discharging or by charging delay lines it is seen that an entirely different principle is employed in this invention, namely the saturation squaring of a high amplitude short pulse from a resonant circuit, which circuit is shocked by a quickly rising current triggered by blocking oscillators.

A very short pulse of good shape is produced with great stability in its duration and in its timing of response to the initial trigger. While specific circuits have been shown the principle of the invention is broader than these specific circuits and the invention should not be deemed limited thereby, but only by the prior art and the spirit of the appended claims.

What is claimed is:

1. A circuit for producing a short duration rectangular pulse for energizing a modulator having a number of modulator tubes, said circuit comprising a switch tube having at least a control grid, a blocking oscillator for producing a sharply increasing voltage on the control grid of said switch tube in response to an input trigger, a primary inductor energized bythe operation of said switch tube, a secondary inductor closely coupled to said primary inductor and adapted to resonate with stray and tube capacitances at a wave length substantially double the desired modulator pulse length, a diode across said secondary inductor for damping out all oscillation subsequent to the first positive voltage swing of said secondary circuit, and a boot strapped driver tube for driving said modulator tubes, and itself adapted to be driven beyond saturation by said positive voltage swing for amplifying and squaring said positive voltage swing, said modulator tubes being adapted to be activated by said amplified and squared output from said driver to produce a pulse adapted to energize a magnetron.

2. A circuit for producing a short duration rectangular pulse for energizing a modulator having a number of modulator tubes, said circuit comprising a switch tube responsive to an input trigger, a primary inductor energized by the operation of said switch tube, a secondary inductor closely coupled to said primary inductor and adapted to resonate with stray and tube capacitances at a wave length substantially double the desired modulator pulse length, means for damping all oscillation in said secondary circuit following the initial positive voltage swing, and a boot strapped driver tube energized by said posi- 4 tive voltage swing to beyond saturation for amplifying and squaring said positive voltage swing said modulator tubes being adapted to be energized by said amplified and squared pulse to produce a pulse adapted to energize a magnetron.

3. A circuit for producing a short duration rectangular pulse for energizing a modulator having a number of modulator tubes, said circuit comprising a switch tube having at least a control rid, a plurality of blocking oscillators in series for producing a sharply increasing voltage on the control grid of said switch tube in response to aninput trigger, a primary inductor energized by the operation of said switch tube, a secondary inductor closely coupled to said primary inductor and adapted to resonate with stray and tube capacitances at a wave length substantially double the desired modulator pulse length, a diode for damping out all oscillation subsequent to the first positive voltage swing of said secondary circuit, and a boot strapped driver tube for driving said modulator tubes, and itself adapted to be driven beyond saturation by said positive voltage swing for amplifying and squaring said positive voltage swing, said modulator tubes being adapted to be activated by said amplified and squared output from said driver to produce a pulse adapted to energize a magnetron.

4. A circuit for producing a short duration rectangular pulse for energizing a modulator having a number of modulator tubes, said circuit comprising a switch tube having at least a control grid, a plurality of blocking oscillators in series for producing a sharply increasing voltage on the control grid of said switch tube in response to an input trigger, a primary inductor energized by the operation of said switch tube, a secondary inductor closely coupled to said primary inductor and adapted to resonate with stray and tube capacitances at a wave length substantially double the desired modulator pulse length, means for damping out all oscillation subsequent to the first positive voltage swing of said secondary circuit, and a boot strapped driver tube for driving said modulator tubes, and itself adapted to be driven beyond saturation by said positive voltage swing for amplifying and squaring said positive voltage swing, said modulator tubes being adapted to be activated by said amplified and squared out-'- put from said driver to produce a pulse adapted to energize a magnetron.

5. A circuit for producing a short duration rectangular pulse for energizing a modulator having a number of modulator tubes, said circuit comprising a switch tube having at least a control grid, a plurality of blocking oscillators in series for producing a sharply increasing voltage on the control grid of said switch tube in response to an input trigger, a primary inductor energized by the operation of said switch tube, a secondary inductor closely coupled to said primary inductor and adapted to resonate with stray and tube capacitances at a wave length substantially double the desired modulator pulse length, a diode for damping out all oscillation subsequent to the first positive voltage swing of said secondary circuit, and a boot strapped driver tube for driving said modulator tubes. and itself adapted to be driven beyond saturation by said positive voltage swing for amplifying and squaring said positive voltage swing.

6. A circuit for producing a short duration rectangular pulse for energizing a modulator having a number of electron tubes, said circuit comprising, a thyratron tube responsive to a trigger pulse, a primary inductor energized by the discharge of said thyratron, a econd inductor closely coupled to said primary inductor and adapted to resonate with stray and tube capacitances at a wave length substantially double the desired modulator pulse length, said first and second inductors being connected in such a manner that the first voltage swing across said second inductor is positive, a diode connected across said second inductor for damping out all oscillation subsequent to the first positive voltage swing across said secondary inductor, and a boot strapped driver circuit energized by said positive voltage swing for driving said modulator tubes, and itself being adapted to be driven beyond saturation by said positive voltage swing for amplifying and squaring said positive voltage swing, said modulator tubes being adapted to be activated by said amplified and squared output from said driver to produce a pulse adapted to energize a magnetron.

7. A modulator circuit for producing a short duration rectangular pulse for energizing a tube of a modulator comprising, a switch tube having at least a control grid, a plurality of blocking oscillators in series for producing a sharply in creasing voltage on the control grid of said switch tube in response to an input trigger, a primary inductor energized by the operation of said switch tube, a secondary inductor coupled to said primary inductor and adapted to resonate with stray and tube capacitances at a wave length substantially double the desired modulator pulse length, a diode for damping out all oscillation subsequent to the first positive voltage swing of said secondary circuit, and a boot strapped driver circuit energized by said first positive voltage swing for driving said modulator tube, said boot strapped driver circuit comprising an electron tube having at least an anode, a control grid and a cathode, a point of reference potential, at source of potential positive with respect to said reference point and connected to said anode, a cathode load impedance connected between said cathode and said reference point and means for coupling said positive voltage swing between said cathode and said control grid of said boot strapped driver tube, said positive voltage swing having a sufiiciently high amplitude to drive said boot strapped driver tube beyond saturation whereby said positive voltage swing appears amplified and squared across said cathode load impedance.

HAROLD L. JOHNSON. VERNAL JOSEPHSON.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,153,202 Nichols Apr. 4, 1939 2,154,783 Stromeyer Apr. 18, 1939 2,237,661 Ernst Apr. 8, 1941 2,244,003 Eaglesfield et a1. June 3, 1941 2,255,882 Hathaway Sept. 16, 1941 2,408,061 Grieg Sept. 24, 1946 2,439,324 Walker Apr. 6, 1948 2,440,278 Labin et a1 Apr. 27, 1948 2,468,058 Grieg Apr. 26, 1949 2,605,409 Forbes July 29, 1952 OTHER REFERENCES Principles of RadarM. I. T. Staff, First Edition, 1944, pages 6-55. Copy in Library of Congress.

Principles of RadarM. I. T. Stafi, 2nd edition, 1946, pages 6-53. 

